The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Wireless communication systems may transmit and/or receive data via radio frequency (RF) signals at various frequencies. For example, conventional Wi-Fi communication systems may include less than a 0.5 gigahertz (GHz) spectrum allocated between 2 GHz and 6 GHz (e.g., 2.4 GHz Wi-Fi). This small spectrum may provide for transmission of, for example, up to 300 megabits per second (Mb/s).
60 gigahertz (GHz) wireless communication systems, on the other hand, may include an unlicensed 7 GHz spectrum centered at or near 60 GHz (e.g., 57-64 GHz). The large 7 GHz spectrum may provide for multi-gigabit (Gb) RF links (e.g., >1.0 Gb/s). For example, multi-Gb RF links may allow for transmission of high-definition (HD) media such as HD video.
60 GHz wireless communication systems may also provide more secure transmissions. More specifically, oxygen attenuates high frequency signals (e.g., 57-64 GHz signals), thus limiting the distance of transmissions. In other words, these high frequency signals may rarely be intercepted by other antennas located beyond an intended target antenna.
Moreover, 60 GHz wireless communication systems may include high gain, narrow beam antennas that accurately transmit these short distances to intended target antennas (i.e., unidirectional, as opposed to wide-beam). 60 GHz wireless communication systems, therefore, may include densely distributed antennas that may transmit at the same frequency with minimal interference and increased security. The large number of unidirectional antennas, however, may result in a lack of “channel reciprocity.”
Channel reciprocity is based on the property that electromagnetic waves traveling in both directions undergo the same physical perturbations (e.g., reflection, refraction, diffraction, etc.). Thus, when an RF link operates at the same frequency band in both directions, the impulse response of the channel observed between any two antennas may be the same regardless of the direction. Application of the channel reciprocity principle, therefore, may remove the necessity for a continuous feedback of channel estimates.
Two stations in a 60 GHz wireless communication system, however, may include different numbers of antennas. Each station, therefore, may transmit at a different power. Moreover, in addition to oxygen attenuation, transmissions between the stations may be affected by precipitation. For example, the effect of rainfall on 60 GHz transmissions may be greater than the effect of oxygen attenuation. For example only, lower data rates may be required during rainfall to achieve a desired throughput. Therefore, multiple modulation and coding schemes (MCSs) may be required depending on operating conditions. For example, an MCS may include a modulation scheme and/or a data rate.
FIG. 1 illustrates a conventional 60 GHz wireless communication system 10. The 60 GHz wireless communication system may include a first node 12 (Station A, or “STA”) and a second node 14 (Station B, or “STB”) that communicate via RF signals. In other words, Station A 12 may transmit and/or receive RF signals to/from Station B 14. Similarly, Station B 14 may transmit and/or receive RF signals to/from Station A 12.
As previously described, Station A 12 and Station B 14 may include different numbers of antennas. For example only, Station A 12 includes 36 antennas and Station B includes 2 antennas. Station A, therefore, may transmit RF signals at a much higher power than Station B. For channel reciprocity to apply, channel metrics in the forward link direction (ρF) equal channel metrics in the reverse link direction (ρR). However, due to different numbers of antennas and thus different MCS and/or data rates that may be used, channel reciprocity may not apply (e.g., ρF≠ρR) in the example communication system of FIG. 1.